Interactions between spatiotemporal dynamics of copepods and hydro-ecological change in marine ranching ecosystems

Marine ecosystems are encountering a variety of environmental challenges as a result of global climate change. In response to these challenges, the development and expansion of marine ranching have emerged as a crucial solution. Notably, zooplankton is acknowledged as an essential indicator for evaluating the ecological health of marine ranching. This study examined the spatiotemporal distribution of copepod abundance and its reaction to environmental factors, utilizing data collected from the marine ranching area of Haizhou Bay (Lianyungang, Jiangsu, China) between 2003 and 2022. The results showed that copepod abundance exhibited a notable pattern, with higher levels in spring compared to summer and autumn, and was consistently distributed uniformly in the central region of the marine ranching area. During El Niño years, copepod abundance was more likely to be found outside the bay, unlike non-El Niño years, where the opposite distribution was noted. The generalized additive model (GAM) revealed that the primary environmental factors influencing copepod abundance across various seasons included temperature, SiO₃⁻–Si, NO₃⁻–N, and Chlorophyll a. However, during El Niño events, the key environmental factors shifted to temperature, NO₃⁻–N, and dissolved oxygen (DO). The study concluded that nutrients influence copepod abundance across different climate conditions. During intense El Niño events, temperature was also found to affect copepod abundance indirectly. It was also noted that diatoms are less likely to directly impact copepod abundance through direct predation–prey interactions. The findings of this study provide valuable insights that can enhance our ability to predict changes in zooplankton populations within marine ranching systems as they respond to global climate change. This knowledge is crucial for conducting thorough assessments of the ecological benefits associated with marine ranching and for guiding its sustainable development. Ultimately, this research's data and scientific references generated from this research will be instrumental in evaluating offshore ecological environments and facilitating practical ecosystem restoration efforts.